The present invention is concerned with a remotely-read energy metering product which is adapted to monitor energy usage and to process energy data for transmission to a remote location over AC power lines in a system of the type shown, for example, in Jagoda U.S. Pat. No. 4,012,734 issued Mar. 15, 1977, for "Synchronous Power Communicating". The device of the present invention is intended to be utilized by electric utilities to perform the functions of measuring the consumption of energy by individual customers of the utility, said measurement being performed at the customer's premises, and to read the measurement remotely by sending signals over the power lines as opposed to having an employee of the utility visit the customer and visually read a watt-hour meter.
Electrical utility companies bill their customers based on the total amount of energy used by the customer. This is ordinarily achieved by placing an energy recording device, i.e., a known form of watt-hour meter, at the customer's residence. Such watt-hour meters have a mechanical display which is read, usually monthly, by an employee of the utility; and the difference between successive month's readings represents the energy used by the customer during a given month, and is the basis for the customer's bill.
Watt-hour meters are commercially available in various constructions. Typically, such meters have sensors which are interconnected with the customer's electrical wiring in such a manner that they will detect both the voltage input to the customer by the utility and the current drawn by the customer. These sensors cause rotation of a metallic disc in the meter, and the angular rotation of the disc is a linear function of the energy, expressed in watt-hours, used by the customer. The angular rotation of the disc drives a series of reduction gears which, in turn, cause the incrementing of a numerical display register.
In recent years, electrical utilities have expressed an increasing interest in metering plans which are more complicated than just metering the total energy used. One approach is to bill the customer at a varying rate for the energy depending upon the time of day the energy is used. Another approach is to use a charge for the speed at which energy is used, called the "demand". The motivation for these alternative approaches is the increased cost associated with generating electricity, and utilities are interested in billing approaches which more accurately reflect the cost of generating electricity. Additionally, many utilities seek to use their billing mechanism as a motivational tool to encourage customer's to change their usage habits in a manner which will make the overall generation of electricity less expensive, i.e., they seek to encourage people, via financial incentives or penalties, to activate "optional" loads at "off-peak" hours.
American Science and Engineering, Inc., of Cambridge, Mass., the assignee of the instant application, manufactures a product line which enables utilities to perform these advanced metering techniques. The operation of this system is generally described in the aforementioned Jagoda et al U.S. Pat. No. 4,012,734, and the system provides the very desirable capability of collecting metering information at a central location by sending signals over the power lines. Signal transmission is in two directions, i.e., an outbound message from the central location causes equipment at the customer's location to generate an inbound message to the central location containing the metering information.
The aforementioned known system utilizes the watt-hour meter as the principal sensor of electrical energy consumption. A device is affixed to the watt-hour meter to generate output signals indicating revolution of the meter disc. Such devices, commonly referred to as pulse initiators, are in themselves well known and may take the form, for example, which is described in Jarva U.S. Pat. No. 4,281,325 issued July 28, 1981, for "Positive Feedback Meter Pulse Initiator". Pulse initiators are commercially available and adapted to be affixed to an existing watt-hour meter or, alternatively, some meter manufacturers offer watt-hour meters with the pulse initiator already built in.
The metering information supplied by a meter/pulse initiator device of one of the types described above can be transferred to a remote location, in response to a command from that remote location, by means of a so-called transponder which is adapted to count pulses thereby to provide the desired metering information, and to perform the function of reading the metering information over the power line. One approach that was originally taken was to supply such a transponder in the form of a separate piece of hardware having male connectors on one side thereof adapted to be plugged into the socket which customarily receives the watt-hour meter, in place of the watt-hour meter itself, the transponder also being provided with an auxiliary set of female connectors into which the male contacts of the meter are plugged, as well as a further connector into which the pulse initiator output lead of the meter can be plugged. This plural pluggable unit arrangement made it generally difficult, however, and often hazardous, to install a meter and an associated transponder and, moreover, required that an objectionably large number of interconnections be made.
In order to obviate the foregoing disadvantages, an alternative unit was disclosed in prior copending Kochem et al U.S. application Ser. No. 279,409 filed July 1, 1981, for "Meter Transponder Hybrid", assigned to the assignee of the present invention, now abandoned. In the Kochem et al arrangement, a single unit was provided which combined the functions of the watt-hour meter, pulse initiator, and transponder, with this single unit taking the form of an integrated structure that is as easy and safe to install as the conventional watt-hour meter. The Kochem et al meter transponder hybrid suffered from the disadvantages, however, that it required fairly extensive modification of the mechanical portions of a commercially available watt-hour meter mechanism, thereby making the meter conversion time consuming and very costly; the overall profile of the modified meter unit was significantly larger than that of a conventionally available watt-hour meter; and the modification of the meter to accept the transponder involved an enlargement of the four blades of the meter, which enlargement caused the conventional current capacity of the watt-hour meter (normally 200 amps) to be derated somewhat.
The present invention provides an improved meter transponder hybrid which exhibits the advantages of the aforementioned Kochem et al unit, but which avoids the disadvantages thereof, i.e., the unit of the present invention exhibits a low overall profile, with no extended blades, and hence has negligible impact on 200 ampere service; there are no alignment problems between the transponder and the meter; no hole is required in the meter base for the pulse initiator wiring; and the overall unit is less expensive to manufacture since it employs an entirely conventional, commercially available watt-hour meter which is used in its unmodified form (except for the addition of the optical head of a pulse initiator, if such a pulse initiator is not already present on the meter). The invention, in effect, provides an electronics package that contains the pulse initiator readout circuit and the transponder electronics in a physical arrangement which is added to the conventional watt-hour meter without requiring any physical change to the meter movement itself and without increasing the overall profile of the meter.